The present invention generally relates to luminaires, and more particularly to luminaires used with grid ceiling systems.
Grid ceiling systems are commonly used in commercial buildings, schools, and other interior structures. Such ceiling systems are created by suspending a T-bar grid from the building's structural ceiling and filling the T-bar grid with ceiling tiles. The T-bar grid is made up of interconnected T-bars that form grid openings for the ceiling tiles, which, when dropped into the grid openings, are supported on the T-bars' bottom horizontal T-walls. The most common dimensions for the grid openings are the two foot by two foot and four foot by four foot for supporting similarly sized ceiling tiles, however, other grid opening dimensions are possible for accommodating different ceiling tile sizes, for example five foot by five foot tiles. Ceiling tiles used in grid ceilings are typically acoustic tiles for enhancing the acoustical environment of the interior space below the grid ceiling.
Customarily, luminaires are provided in the grid ceiling system for general illumination. Luminaires adapted for this use are called troffers, and are typically fluorescent luminaires having fluorescent light sources, however, other light sources, such as incandescent and HID lamps are sometimes used. Troffers are sized in correspondence with the grid openings of the T-bar grid and are mounted in selected grid openings instead of a ceiling tile. (The number and distribution of the troffers on the grid ceiling depend on the type of troffer used and the general lighting requirements of the space.) Parabolic troffers and lens troffers are currently the most common luminaires designed for T-bar grid mounting; however, other types of troffers are commercially available, for example, troffers with a secondary perforated reflector under the lamps.
The physical dimensions of the lamps, lamp sockets, and optical components used in conventional troffers require that the troffer have a minimum height. While the height of commercially available troffers varies, most have a height of at least three inches. Thinner troffers have been designed for T-5 fluorescent lamps, which have a relatively small diameter (⅝ inches), but the component dimensions of such troffers would still impose a lower limit on the height on the troffer. Generally, troffer heights less than about 1½ inch would be difficult to achieve.
The height of a troffer can have important implications in the shipment, installation, use, and ultimately the disposal of the troffers. For example, the height of the troffer determines its volume and the greater the volume the greater space and packaging material that will be needed to ship the troffers. The presence of the troffers in the grid ceiling must also be taken into account when determining the space required between the grid ceiling system and the building's overhead structural ceiling. The space between the top of the troffers and the structural ceiling has to be adequate to accommodate HVAC and fire alarm systems, sprinkler piping, and other utilities in the building. Use of conventional troffers, which have a depth that causes the troffers to protrude significantly above the grid ceiling, adds to this space requirement. This added space requirement can be meaningful in terms of building construction costs. For example, a reduction of three inches in the requirement for the space above the grid ceiling will translate to three inches less in the requirement for the separation between the building's structural floors and structural ceilings. This can, in turn, result in less material required to construct the building due to a reduction in overall building height. Or it can possibly allow for an additional floor being added to a high rise building. For example, a three inch saving in the space above the grid ceiling will allow a floor to be added to a 40-story high rise building normally having a structural floor to structural floor dimension of 10 feet.